Sound monitor intruder alarm system



May 19, 1970 L. A. STEVENSON, JR, E

SOUND MONITOR INTRUDER ALARM SYSTEM 3 Sh eets-Sheet 2 Filed Aug. 8, 196? Lou 0. M/ck/ey,/r. Law: A. Sfe vensonL/r.

INVENTURS B W & 0m

ATTORNE YS May 19, 1970 L. A. STEVENSON, JR, EFAL $513,463

SOUND MONITOR INTRUDER ALARM SYSTEM 3 Sheets-Sheet 3 Filed Aug. 8: 1967 \EQQY M A hm A00 3. flf/cAk y, Ci 00/. A. Jze V6030, 4/

INVENTORJ B) M, (My/v & 0m JTTURNEYS No. 659,067 I Int. Cl. G08b 13/16 US. Cl. 340258 8 Claims ABSTRACT OF THE DISCLOSURE An intruder alarm system which is activated by either the sounds made by an intruder or the changein-thm Pa atbaprotectedareacaused by hang siglpgsitigrpf objects in the area. A sound pattern is esta 1s ed in the prom a suitable sound source. Means are provided to monitor the sound pattern and generate a DC. voltage which is proportional to the sound pattern. Changes in the D.C. voltage are registered by a sensitive level change detector. Alternatively, means are provided to produce quantized electrical pulses in response to the changes in the DC. voltage. The electrical pulses are applied to an integrator means which activates an alarm when a certain number of pulses are received in a unit of time. Means are provided to produce electrical pulses in response to noises other than the sound pattern. These pulses are also applied to the integrator means.

BACKGROUND OF THE INVENTION This application is a continuation-in-part of application Ser. No. 578,603, tiled Sept. 12, 1966, and now abancloned.

This invention relates to sound actuated alarm apparatus, and more particularly to alarm apparatus installed in protected area and responsive to either sounds or changes in sound patterns caused by the presence of an intruder.

Conventional intruder alarm systems which are actuated by the opening of a window or door are somewhat unreliable because a careful intruder can often prevent actuation of the alarm. A sound actuated alarm system is much less susceptible to being foiled by an intrduder. However, such a system must be designed so that normal sounds from a clock or refrigerator, for example, do not set off the alarm.

Copending and coassigned applications Ser. No. 369,232, filed May 21, 1964, and Ser. No. 610,069 filed Jan. 18, 1967, and now abandoned, disclose sound alarm systems including means for preventing alarms due to normal noises. The systems include a plurality of transducers in the protected area and an alarm electrical circuit channel for amplifying and quantizing signals generated by the transducers. The quantized signals are passed through a relay or gate circuit to an integrating circuit means which actuates an alarm in response to a given number of quantized signals within a unit of time. The relay or gate circuit is controlled by signals from a cancel channel so that quantized signals of normal or background noises are not transmitted to the integrator circuit. Transducers are positioned in the protected area to monitor the normal background noise, and the signals generated by these transducers are amplified and quantized by the cancel channel. The quantized pulses from the United States Patent ICC cancel channel are then applied to the gating circuitry to render the gate nonconductive and thus preventing actuation of the alarm.

The present invention is a system which is responsive to either the noises of an intruder or the changes in the sound pattern in the protected area caused by changes in position of objects in the area, such as the movement of an intruder.

SUMMARY OF THE INVENTION The present invention is an improved sound operated alarm apparatus which is actuated either by the sounds of an intruder or changes in the existing sound pattern caused by movement in the protected area. A sound pattern at a preselected frequency is established in the protected area by a suitable sound source. The alarm apparatus includes means for monitoring the sound pattern and detecting changes therein. A sensitive level change detector is provided to indicate an alarm or generate a quantized pulse in response to changes in the sound pattern. Means is also provided to operate the alarm if the sound pattern disappears due to failure of the sound source. The alarm apparatus also includes means for detecting sounds of an intruder. Included is a filter means for attenuating the sound generated by the sound source and low frequency sounds from outside sources which may penetrate the walls of the protected area. Higher frequency sounds which are characteristic of forcing or breaking are passed to detecting means and then quantized so that equal importance is attached to noises of long or short duration and large or small amplitude. A given number of quantized pulses from either the noise detecting means or the sound pattern monitoring means within a unit of time will actuate the alarm.

The invention will be more fully understood from the following detailed description and appended claims when taken with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS Referring now to FIG. 1 of the drawings, one embodiment of the invention is illustrated in block form. A sound pattern is established in the protected area by a sound source 1 which includes a three kilohertz oscillator and speaker. A plurality of transducers 2 are positioned in the protected area to receive the sounds from the sound source. The transducers can be conventional microphones and the number of units wil depend upon the size and nature of the protected area. Electrical signals generated by the transducers are passed to a narrow band amplifier 3 which is tuned to the frequency of the sound source. The amplifier is a conventional multi-stage unit having filter means for passing only the sound pattern frequency.

The output of amplifier 3 is connected to an envelop de-.

tector 4 which produces a DC. voltage proportional to the standing wave or sound pattern in the protected area.

Patented May 19, 1970 The D.C. voltage is applied to a conventional D.C. amplifier 5, and the amplifier is connected to a level change indicator 6. The indicator includes meter means for comparing the detected D.C. voltage with a reference voltage. Preferably, the meter means is located in a guard station where it can be continually monitored.

Any motion or change of position of objects in the protected area will change the standing waves or sound pattern in the area, and this change in sound pattern causes a change in the D.C. voltage produced by the detector. The meter in the level change indicator registers the change in voltage. The level change detector maintains the reading until the reference voltage is reset by a guard. The indicator may also actuate an alarm.

FIG. 2 is a detailed schematic of the alarm apparatus shown in FIG. 1. The circuits are conventional and will not be discussed in detail. Again, the sound source 1 is illustrated in block form. The electrical signal from one of the transducers 2 is capacitively coupled to the narrow band amplifier. The two stage tuned amplifier includes NPN transistors and 11 with a three kilohertz tuned twin T filter 12 providing a feedback loop between the collector of transistor 11 and the emiter of transistor 10. The amplifier is connected through an emitter follower circuit including transistor 13 to the envelop detector. The

cluding transistor 17 is controlled by the bias voltage from potentiometer 18. Thus, by adjusting the setting of potentiometer 18, a reference voltage is generated at the collector of transistor 17 which is made equal to the normal amplified D.C. voltage at the collector of transistor 16. The level change indicator including transistors 20 and 21 is connected between the two amplifiers so that bias voltage for transistors 20 and 21 are derived from the two amplifiers. Meter 22, a D.C. voltmeter, for example, is connected between transistors 20 and 21 and indicates when the bias voltages to the two transistors are out of balance; i.e. when a change in the sound pattern occurs. Transistor 23 provides a feedback loop between the level change indicator and the D.C. amplifiers.

FIG. 3 is a block diagram of another embodiment of the invention which includes a sound pattern monitoring channel and a noise detecting channel. Again, a sound pattern is established in the protected area by sound source 1 which includes a three kilohertz oscillator and speaker. A plurality of transducers 2 are postion within the protective area to pick up the sound pattern and any nected to the sound pattern monitoring channel and to the noise detecting channel. The sound pattern monitoring channel includes an amplifier 31 which is tuned to amplify only the three kilohertz signal. The tuned amplifier 31 is connected to a detector-amplifier 32 which develops a D.C. voltage corresponding to the three kilohertz signal envelope. A pulse circuit 33 is connected to the detector-amplifier and generates a positive pulse in response to either positive or negative changes in D.C. voltage from detector-amplifier 32. The positive pulse triggers a monostable multivibrator 34 which delivers a quantitized pulse to integrator 35 in response to each change in the sound pattern. A Schmitt trigger circuit 36 is connected to the output of amplifier 31 and delivers a charging current to the integrator 35 if the output of amplifier 31 should disappear due to failure of the sound source.

The noise detector channel includes a filter 40 which filters out the three kilohertz signals from the preamplifier 30. The filtered signal is applied to amplifier 41 which includes an automatic gain control circuit 42. The action of the automatic gain control circuit adjusts the gain of the amplifier so that background noise will almost trigger the alarm, thus maximum sensitivity is provided at all times even with varying background noise levels. Amplifier 41 is capacitively coupled to detector 43 which develops a D.C. voltage in response to changes in the signals from the amplifier. The detector is capacitively coupled to a monostable multivibrator 44.

Multivibrator 44 is connected to integrator 35, and pulses from multivibrator 44, along with pulses form multivibrator 34 of the pattern monitoring circuit, charge the integrator. The integrator is designed to trigger a Schmitt trigger circuit 36 when a given number of pulses are received by the integrator in a unit of time, e.g. three pulses in thirty seconds. When trigged, the Schmitt trigger 36 activates alarm 37.

FIG. 4 is a detailed schematic diagram of the alarm apparatus shown in the block diagram of FIG. 3. Again, the individual circuit portions of the apparatus are relatively conventional, and each circuit is not discussed in detail.

Signals generated by one of the transducers 2 are coupled through capacitor to transistors 51 and 52 of the preamplifier. The output of the preamplifier taken at the collector of transistor 52 is applied to the three kilohertz amplifier in the pattern monitoring channel. The two stage amplifier includes transistors 53 and 54 with a three kilohertz twin '1 filter feedback loop connected between the collector of transistor 54 and the emitter of transistor 53. The output of the amplifier is applied through emitter-follower transistor 56 and capacitor 62 to the low frequency detector-amplifier including transistors 57 and 58. The output of the detector-amplifier is connected to transistor 59 which provides out of phase signals at its collector and emitter in response to changes in the D.C. voltage from the detector-amplifier. Both the emitter and collector of transistor 59 are capacitively coupled to diodes 60 and 61 which provide positive trigger pulses in response to either positive or negative changes in the D.C. voltage from the detector-amplifier. The trigger pulses are applied to the monostable multivibrator including transistors 63 and 64. Pulses generated by the multivibrator are passed through variable resistor 65 to the integrator-capacitor 66.

The Schmitt trigger including transistors 67 and 68 is connected to the output of emitter-follower transistor 56 to monitor the presence of three kilohertz signal. When- -ever the three kilohertz signal is removed, the Schmitt trigger changes state and provides a charging current to the integrator-capacitor 66.

In the noise detecting channel, the three kilohertz twin T filter 70 is connected to the preamplifier through potentiometer 71. The filter is connected to a two stage amplifier including 72 and 73. The output of the amplifier taken at the collector of transistor 73 is passed through emitter-follower transistor 74 to a detector circuit including diodes 75 and 76.

The automatic gain control circuit for the amplifier is also connected to the emitter-follower transistor 74 and includes amplifier transistor 77 which is connected through the emitter-follower transistor 78 to a detector including diodes 79 and 80. The D.C. voltage generated by the detector controls transistor 81 which is connected to diodes 82 and 83 and establishes the bias voltage level for the amplifier transistor 72.

The D.C. voltage envelope developed by diodes 75 and 76 is applied through a small capacitor 85 to the mono stable multivibrator which includes transistors 86 and 87. Because of its low capacitance, the capacitor 85 requires a fast rise on the envelope of the sound, thus making it a sharp sound recognizer. The capacitor also functions as a differentiator and applies only one trigger pulse to the multivibrator in response to each noise picked up by the transducers.

The pulses generated by the monostable multivibrator cluding transistors 91 and 92 changes state and activates the alarm 93 and alarm light 94 through emitter follower transistors 95 and 96. Integrator-capacitor 66 is provided with a leakage path through diode 97, resistor 98 and resistor 99. Once a suflicient charge is built up in the capacitor 66 to cause an alarm, the high voltage devell oped at the emitter of transistor 96 prevents further discharge of the capacitor through this leakage path. The capacitor must then discharge through relatively large i resistor 100. When the voltage across the capacitor 66 drops to a lower trip point, the circuit resets. Alarm time in practice may be from a few seconds to five minutes or more.

While the invention has been described with reference to specific embodiments, the description is illustrative and is not to be construed as limiting the scope of the invention.

I What is claimed is: 1 1. An intruder alarm apparatus comprising: .l sound producing means for establishing a so u r i patl tern in a protected area, A

transducer means placed in said protected area for detecting sounds including said sound pattern and gencrating electrical signals proportional to said sounds, a first circuit means for monitoring said electrical signals for changes therein caused by changes in said sound pattern and generating quantized electrical pulses in response to said changes,

a second circuit means including means for attenuating said signals proportional to said sound pattern and generating quantized electrical pulses in responses to noises of an intruder,

an integrating circuit means connected to receive the quantized pulses from said first and second circuit means and providing a D.C. output voltage the mag- 5 nitude of which is representative of the number of pulses received per unit of time, and

an alarm circuit for giving an alarm when said voltage reaches a preselected maximum.

2. An intruder alarm apparatus in accordance with claim 1 wherein said first circuit means includes:

an amplifier circuit connected to saidtransducer means and tuned to amplify only said sound pattern, i a detector circuit connected to said amplifier circuit for producing a D.C. voltage corresponding to the envelope of the amplified signals,

a pulse circuit connected to said detector circuit for producing electrical pulses in response to changes in said D.C. voltage, and

a quantizing circuit means for receiving said electrical pulses from said pulse circuit and producing an electrical pulse of a uniform duration in response to each pulse from said pulse circuit.

3. An intruder alarm apparatus in accordance with claim 1 wherein said second circuit means includes:

filter means connected to said transducer means for attenuating said signals proportional to said sound pattern,

amplifier circuit means connected to said filter means for amplifying electrical signals proportional to sounds of an intruder,

detector circuit means connected to said amplifier circuit means for producing a D.C. voltage in response to signals from said amplifier, and

quantizing circuit means connected to said detector means for producing electrical pulses of a uniform duration in response to changes in said D.C. voltage.

4. An intruder alarm apparatus as defined by claim 1 wherein said integrating circuit means includes a capacitor and a resistive circuit shunting said capacitor, and said alarm circuit includes a trigger circuit which changes state and produces an output voltage when the electrical charge on said capacitor exceeds a preselected value.

5. An intruder alarm apparatus comprising the combination of sound producing means for establishing a sound pattern in a protected area,

transducer means placed in said protected area for detecting sounds including said sound pattern and generating electrical signals proportional to said sounds,

a first circuit means for monitoring said sound pattern and including,

an amplifier connected to said transducer means and tuned to amplify only said sound pattern,

a detector circuit connected to said amplifier circuit for producing a D.C. voltage correspondingto the envelope of the amplified signals,

a pulse circuit means connected to said detector circuit for producing electrical pulses in respouse to changes in said D.C. voltage, and

a quantizing circuit means for receiving said electrical pulses from said pulse circuit and producing an electrical pulse of uniform duration in response to each pulse received by said pulse circuit,

a second circuit means for detecting sounds gfan intruder including,

' filter means connected to said transducer means for attenuating electrical signals proportional to the sound pattern and passing electrical signals proportional to other sounds,

amplifier circuit means connected to said filter means for amplifying electrical signals passed by said filter means,

detector circuit means connected to said amplifier circuit means for producing a D.C. voltage in response to signals from said amplifier, and

quantizing circuit means for receiving said D.C.

voltage and producing an electrical pulse of uniform duration in response to changes in said D.C. voltage,

integrator circuit means connected to said first circuit means and said second circuit means for integrating said pulses from said quantizing circuit means and providing a D.C. output voltage the magnitude of which is representative of the number of pulses received per unit of time, and level sensing means connected to said integrator circuit means for responding to said D.C. output voltage by initiating an alarm When said D.C. output voltage reaches a predetermined level.

6. An intruder alarm apparatus as defined by claim 5 wherein said level sensing means includes a trigger circuit which changes state and produces an alarm activating voltage when said D.C. output voltage reaches a predetermined level.

7. Apparatus in accordance with claim 5 wherein said integrating circuit means includes:

a capacitor,

a charging circuit for said capacitor,

said charging circuit being connected to said quantizing circuit means of said first and said second circuit means,

and a resistive circuit connected in parallel circuit relationship with said capacitor.

8. Apparatus in accordance with claim 5 wherein said first circuit means further includes a trigger circuit connected between said amplifier circuit of said first circuit means and the integrating circuit means and which provides a charging current to said integrating circuit means upon the disappearance of the sound pattern signal from said amplifier circuit.

References Cited UNITED STATES PATENTS Miessner 340258 Bagno.

Chapin 340258 Roberts 340258 8 5/1964 Kelly et a1 340258 X 9/1966 Hansen 340258 X US. Cl. X.R. 

